A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. The mechanical energy can further be used to produce electricity. A wind turbine can rotate about either a horizontal axis or a vertical axis. A wind turbine that rotates about a horizontal axis is referred to as a horizontal axis wind turbine, and a wind turbine that rotates about a vertical axis is referred to as a vertical axis wind turbine.
A horizontal axis wind turbine typically has a main rotor shaft and electrical generator at the top of a tower, where the main rotor shaft is commonly pointed into the wind to generate electric power. Oftentimes, a blade of a horizontal axis wind turbine continuously produces power in a revolution around a rotation axis. Further, horizontal axis wind turbines are conventionally controlled in various manners. For instance, a speed at which blades of a horizontal axis wind turbine rotate is oftentimes controlled by a connection to an electrical grid. Moreover, torque produced by the horizontal axis wind turbine can be controlled by pitching the blades of the horizontal axis wind turbine. According to an example, a control system of a horizontal axis wind turbine can adjust blade pitch to maintain the torque of the rotor to be within operating limits as wind speed changes. Following this example, the blades of the horizontal axis wind turbine can be feathered, where an angle of attack is minimized by turning the blades to be parallel to airflow, to stop the machine when wind speed exceeds a maximum cut-out speed.
In contrast to a horizontal axis wind turbine, a vertical axis wind turbine has a main rotor shaft arranged vertically; thus, the vertical axis wind turbine need not be pointed into the wind to operate. As opposed to continuously producing power through a revolution, a blade of a vertical axis wind turbine produces power in two bursts within a revolution around the rotation axis (e.g., the blade sweeps through the air in an upwind pass and a downwind pass). However, significant pulsatory torque can be produced during each revolution of a blade in the upwind and downwind passes, which can result in machine fatigue. Further, conventional vertical axis wind turbines can be prone to damage due to going into overspeed (e.g., if a connection with an electrical grid is lost or a brake of the vertical axis wind turbine fails). Often, conventional blade pitching used for horizontal axis wind turbines may be unable to be employed for vertical axis wind turbines.